CALCIUM  CARBIDE  AS  A METALLUR- 
GICAL REDUCING  AGENT 


BY 


SAMUEL  COHN 


THESIS 

FOR  THE 


DEGREE  OF  BACHELOR  OF  SCIENCE 


IN 

CHEMICAL  ENGINEERING 


COLLEGE  OF  LIBERAL  ARTS  AND  SCIENCES 


UNIVERSITY  OF  ILLINOIS 


dQ>Q, 


UNIVERSITY  OF  ILLINOIS 


J"  ^ o - *-« 

: - a'-*:'  ^ ig2fj 


THIS  IS  TO  CERTIFY  THAT  THE  THESIS  PREPARED  UNDER  MY  SUPERVISION  BY 


ENTITLED 


k.u 


IS  APPROVED  BY  ME  AS  FULFILLING  THIS  PART  OF  THE  REQUIREMENTS  FOR  THE 

DEGREE  OF  

in 

A-t  _ JE'ii  ^X.  I i'S  T_i  I 

Instructor  in  Charge 

Approved  : 

HEAD  OF  DEPARTMENT  OF 




Digitized  by  the  Internet  Archive 
in  2015 


https://archive.org/detaiis/calciumcarbideasOOcohn 


ACKHOWL3DGM13NT 

The  author  takes  great  pleasure  in  acknowledging 
his  indebtedness  to  Assistant  Professor  W,  S, 
Putnam  for  his  invaluable  advice  throughout  the 
preparation  of  this  thesis. 


Contents 


Introduction 

The  purpoee  of  this  article 

History 

The  preparation  of  oaloium  carbide  2 

Properties  of  calcius  carbide  2 

Reactions  of  calcium  carbide  with  metallic  oxides  4 


Pago 

1 


Effects  of  sulphur  and  phosphorus  in  steel 
Present  methods  employed  in  removing  sulphur 
from  steel 

Experimental 


Analyses  of  the  unreduced  sulphur  remaining 
in  the  fusions 

Summary 

Bibliography 


6 


Determinat 

ion  of 

the 

purity 

of 

calcium 

carbide 

9 

Dotorminat 

ion  of 

the 

purity 

0 f 

ferrous 

sulphide 

10 

Procedure 

in  m a k 

i n g 

a fusion 

of 

calcium 

and 

ferrous  su 

1 p h i d e 

10 

1 1 
1 5 

17 


CALCIM  CARBIDE  AS  A IfflTALLURGIGAL  REDUCING  AGENT 


INTRODUCTION 

The  diaulphuri.'sation  of  sulphide  ores  or  pig  iron  by  a sim- 
ple process  of  oxidation  is  very  far  from  complete.  But  if  disul- 
phurization  is  to  be  thorough,  it  must  be,  by  converting  the  sulphur 
into  calcium  sulphide,  -which  is  universally  carried  out  at  present  by 
adding  lime  to  the  molten  mass  of  impure  metal;  the  reaction  takes 
place  in  the  following  manner: 

PeS  + CaO  + C = CO  + Pe  + CaS, 

The  CaS  is  then  removed  by  the  slag. 

In  this  work,  the  object  is  to  remove  the  sulphur  as  CaS,  j 
but  it  differs  from  the  ordinary  method,  in  that  0aC2  is  employed  in  | 

I 

place  of  CaO.  This  is  to  be  carried  out  by  heating  iron  sulphide  | 
with  the  carbide  at  some  definite  high  temperature,  the  iron  sulphide | 
acting  as  a representative  sulphide  ore.  In  narrowing  down  the  pur-  | 
pose  of  this  work  to  the  most  concise  wording,  it  is  to  study  the  re- | 
actions  of  calcium  carbide  with  ferrous  sulphide,  and  determine 
whether  these  reactions  can  be  applied  in  desulphurizing  steel. 


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HISTORICAL. 


i’rom  tlie  earliest  date  in  the  history  of  metallurgy  it  has 
been  recognized  that  sulphur  and  phosphorus  are  haimful  elements  in 
steel,  and  the  problem  of  their  elimination  has  not  been  thoroughly 
solved,  Among  the  many  methods  and  reagents  that  have  been  employed, 
comparatively  little  has  been  done  with  calcium  carbide. 

It  seems  advisable  to  state  the  manufacture,  properties, 
and  reactions  of  calcium  carbide  now,  so  that  the  reader  will  under- 
stand why  certain  methods  of  attack  have  been  used  later  on, 

Calciuia  carbide  was  first  prepared  by  Woehler  in  1862,  by 

1 

heating  an  alloy  of  zinc  and  calcium  to  a welding  temperature.  It 
was  not  until  Wilson’s  discovery  in  1892  that  it  could  be  commercial- 
ly manufactured  in  the  electric  furnace.  This  process  consists  of 
heating  a mixture  of  finely  pulverized  limestone  and  coke,  in  an  e- 
lectric  arc  at  a temperature  of  1600  degrees  centigrade.  The  re- 
action which  takes  place  in  the  furnace  is  as  follows: 

CaO  + 3c  • CaC2  + GO  — 105350  calories. 

Theoretically,  this  reaction  would  require  a mixture  of  875  parts  by 
weight  of  lime  to  5^3  parts  of  carbon,  but  in  actual  practice  about 
650  parts  of  carbon  are  needed,  since  some  of  it  is  consumed  in  other 
ways  than  by  the  above  reaction. 

The  carbide  as  taken  from  the  electric  furnace  is  hard  and 
crystalline,  but  loses  its  luster  on  exposure  to  air,  especially  when 
moist,  and  finally  crumbles  to  a gray  powder,  containing  many  graph- 
ite particles.  It  may  be  kept  unchanged  in  a well  closed  bottle; 

best  in  the  presence  of  coal-oil.  When  pure,  it  is  colorless,  but 

2 

small  amounts  of  foreign  matter  render  it  reddish  brown  or  black. 


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The  specific  gravity  is  2.3  and  the  melting  point  is  in  the  neighbor- 
hood  of  l800  degrees  centigrade.  It  is  easily  decomposed  by  water  to 
form  calcium  oxide  and  acetylene,  the  chemical  equation  being  as  fol- 
lows: 

CaC2  + H2O  = C2H2  + GaO. 

Theoretically,  one  pound  of  carbide  should  require  .525  pounds  of 
water  for  its  decomposition  and  the  products  formed  should  be  1,156 
pounds  of  lime  and  ,4064  pounds  or  5»535  cubic  feet  of  acetylene  at 
zero  degrees  centigrade,  But  on  account  of  the  impurities,  the  best 
results  obtained  have  been  5 Gu,  Ft.  of  acetylene.  Upon  decomposi- 

4 

tion  of  one  pound  of  the  carbide,  ^00  B.T.U,  are  liberated. 

If  the  carbide  is  heated  in  hydrogen,  a little  tarry  matter 
and  a slight  white  sublimate  are  formed,  but  it  is  otherwise  unalter- 
ed, even  after  long  heating.  Heated  in  air,  the  same  tarry  substance 
is  formed,  but  no  other  action  is  apparent;  even  with  oxygen,  the 
carbide  is  unaffected  until  a very  high  temperature  is  attained,  when 
the  materials  glow  brightly,  yielding  a white  powder. 

Hydrochloric  acid  has  no  action  in  the  cold,  but  on  heating 
it  causes  the  carbide  to  swell  up  and  become  dirty  gray.  A small 
quantity  of  colorless  liquid  distills  over,  white  fiames  are  evolved, 
and  a part  of  the  solid  fuses,  being  converted  into  calcium  chloride. 
Chlorine  is  also  without  action  in  the  cold;  at  a tempera- 
ture of  245  degrees  G,  it  causes  the  carbide  to  glow  brightly,  to 
swell  and  to  fuse  together,  while  a slight  yellowish- white  sublimate 
is  formed;  the  fused  mass  is  calcium  carbide.  Bromine  reacts  at 
350  degrees  C.,  and  sulphur  vapors  at  500  degrees  G,  The  products  of 
the  last  reaction  are  calcium  sulphide  and  carbon  disulphide.  Pe- 
troleum, benzine,  carbon  disulphide  and  carbon  dioxide  do  not  have 
any  effect. 


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Strong  sulphuric  acid  in  the  cold  gives  a few  hubbies  with 
calcium  carbide,  but  on  heating,  the  action  is  increased  and  contin- 
ues after  the  source  of  heat  has  been  removed.  Strong  nitric  acid 

I 

produces  red  fumes,  but  the  gases  from  this  and  from  the  sulphuric 
acid,  burn  with  a luminous  flame.  A solution  of  sulphuric  acid  and 
potassium  bichromate  react  violently  with  the  carbide,  forming  a non- 
inflammable  gas.  The  carbide  acts  as  a reducing  agent  to  many  oxides 
and  if  present  in  excess,  tends  to  allow  the  calcium  to  combine  with 
the  reduced  metal.  In  this  manner,  alloys  with  iron  and  other  metals  t 
are  fomed.  Iron  containing  calcium,  approaches  in  appearance,  that 
of  ferro  manganese,  being  more  brittle  and  easily  oxidisable  in  con- 

5 

tact  with  water. 

If  an  excess  of  litharge  be  heated  to  redness  in  contact 

with  the  carbide  in  a clay  crucible,  the  reaction  is  accompanied  by 

vivid  incandescence,  resulting  in  the  formation  of  metallic  lead  and 

calcium  oxide;  but  with  certain  calculated  proportions  of  the  lith- 

arge  and  carbide,  an  alloy  of  lead  and  calcium  is  formed  which  is 

more  or  less  brittle,  having  a melting  point  lower  than  pure  lead.  | 

Stannic  oxide,  cupric  oxide,  and  ferric  oxide  at  high  tern-  | 

peratures  are  readily  reduced,  giving  results  of  no  practical  value. 

In  a further  operation,  oxides  of  manganese,  nickel,  cobalt,  chromium, 

6 

molybdenum,  and  tungsten  were  readily  reduced,  yielding  calcium  alloyi  . 

Since  calcium  carbide  is  a deoxidizing  agent,  it  will  there- 
fore, when  added  to  a metal  in  the  state  of  fusion  which  is  always 
slightly  oxidized,  react  in  the  following  manner: 

(1)  CaC2  + 2M0  = 2C0  + Ca  + 2M. 

It  is  evident  that  under  these  conditions,  as  one  part  of  the  car- 
bide only  takes  part  in  the  above  reaction,  the  utilization  of  this 
compound  is  not  to  the  best  advantage.  To  increase  its  power,  a 


7 

metallic  chloride,  RCl,  which  must  toe  dehydrated,  may  toe  added;  the 
Cl  will  comtoine  with  the  Ca  set  at  liberty,  in  such  a manner,  that 
the  two  affinities  of  the  C for  the  0,  and  of  the  Ca  for  the  Cl,  will 
act  simultaneously,  giving  the  following  reaction; 

(2)  CaC2  + 2RC1  + 2M0  = 2R  + 2M  + CaCl2  + 2C02* 

These  reactions  may  toe  applied  either  to  the  extraction  of  a metal 
from  its  ores,  or  for  the  manufacture  of  metallic  alloys,  according  tc 
whether  the  metallic  chloride  used  corresponds  with  the  metal  or  not. 

If  M=R,  we  obtain  the  metal  only;  if  not,  we  obtain  the  alloy  R + 2M. 

As  an  example  of  this  formula  we  can  give  the  preparation  of  aluminum 
bronze,  which  consists  of  gently  heating  a mixture  of  alumina  and 
chloride  of  copper,  in  contact  with  calcium  carbide. 

In  an  article  taken  from  the  Journal  of  Society  of  Chemi- 
cal Industry  (1902,  page  1302)  the  above  reactions  (l)  and  (2)  are 
stated  to  react  in  the  following  proportions  toy  Heuman; 

(3)  CaC2  + 3MgO  = 3M2  + CaO  + 2C0 . 

(4)  2MC1  + 2M2  + CaC2  = 3M2  + CaCl2  + 2C0 . 

But  Kugelgen  said  that  the  above  reactions  take  place  as  follows: 

CaC2  + 5M2O  ~ ^®2  CaO  + 5M2  and 
2MC1  + 4M2O  CaC2  — 5M2  CaCl2  ^ 2C02» 

Alumina  which  cannot  toe  reduced  toy  cartoon  even  at  a white  heat,  is 
reduced  toy  the  carbide  in  the  following  manner; 

Alp03  + CaCg  = 2A1  + 2C0  CaO. 

Calcium  carbide  is  also  a reducing  agent  for  many  sulphides. 
Pyrites,  tetrahedrites,  galena,  stitonite,  and  magnesium  sulphide  are 
all  reduced  when  heated  with  the  carbide  in  an  electric  furnace,  leav- 
ing calcium  sulphide;  tout  all  the  metals,  except  the  iron  of  the  py- 
rites, and  the  copper  of  tetrahedrite  are  volatilized.  Aluminum  sul- 

8 

phide  is  not  reduced  when  thus  treated. 


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It  may  seem  from  the  first  paragraph  of  this  article  that 
phosphorus  and  sulphur  have  no  heneficial  effects  when  present  in 
iron  or  steel,  but  to  be  sure,  they  have  their  virtues  as  they  have 
faults,  of  course,  the  latter  being  considerably  more  numerous  than 
the  former,  phosphorus  is  probably  the  most  injurious  impurity  found 
in  steel  with  the  possible  exception  of  the  occuluded  gases  such  as 
oxygen,  hydrogen,  and  nitrogen.  The  ill  effects  of  phosphorus  are 
very  apparent  when  the  steel  is  cold.  It  produces  the  phenomena  of 
"cold  shortness"  or  brittleness  when  cold,  either  in  hardened  or  an- 

9 

nealed  steels.  This  brittleness  is  especially  noticeable  when  the 
steels  are  subjected  to  vibratory  stresses  or  to  shock.  The  ductili- 
ty is  very  little  affected  when  the  loads  are  slowly  applied.  Exper- 
iments have  proven,  that  in  amounts  up  to  .12  per  cent,  phosphorus 
increases  the  strength  under  slowly  applied  loads.  Under  shock  how- 
ever, this  material  was  a failure.  The  bad  effects  of  phosphorus  in- 
crease as  the  carbon  content  is  increased,  due  to  the  formation  of 
coarse  crystals  which  tend  to  produce  brittleness. 

Phosphorus  produces  a phosphide  of  iron,  Ee3P,  which  forms 
a series  of  alloys  with  iron.  The  eutectic  of  this  series  contains 
69  per  cent  of  the  phosphide  or  10.24  per  cent  of  phosphorus,  and  is 
very  brittle.  A small  amount  of  phosphorus  will  dissolve  in  the  iron, 
forming  no  brittle  eutectic,  but  as  the  carbon  is  increased,  it  pre- 
cipitates the  phosphorus  from  the  solid  solution  into  the  brittle 
eutectic  form.  Thus  the  lower  the  carbon,  the  more  phosphorus  may  be 
present  without  being  seriously  injurious. 

Phosphorus  increases  the  tensile  strength  of  steel  somewhat 
as  does  carbon,  but  does  not  decrease  the  ductility  as  rapidly  as 
does  carbon.  Phosphoretic  steels  resist  wear  better  than  steels  with 
a lower  phosphorus,  and  high  phosphorus  is  permissable  or  even  desir- 


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able  If  the  steel  is  to  resist  abrasion  only,  and  no  shock  or  vibra-  | 
tion  is  to  be  encountered*  phosphorus  increases  the  hardness  of 
steel  without  lowering  the  electric  conductivity  as  much  as  other  j 
hardening  elements.  For  this  reason,  high  phosphorus  steels  are  used! 
for  third  rails  of  trolley  systems. 

High  phosphorus  steels  are  used  for  screw  machine  products,  j 
where  shock  strength  is  not  a requisite,  as  it  gives  excellent  ma- 
chining properties,  producing  clean  bright  surfaces,  and  increasing 

I 

the  tensile  strength.  ! 

I 

Sulphur  occurs  in  commercial  steels  as  manganese  sulphide,  | 
and  when  manganese  is  absent  the  sulphur  is  present  as  FeS,  of  which 
the  former  sulphide  is  a less  harmful  constituent;  the  reason  being 
that  FeS  spreads  out  in  webs  or  sheets  instead  of  coalescing  in  drops 

I 

as  MnS  does.  Steels  for  several  purposes  such  as  that  used  for  long- 
itudinal strength  are  benefited  by  a certain  amount  of  manganese  sul- 
phide; sulphur  in  low  carbon  steels  improves  the  free  cutting  proper- 
ties. Sulphur  is  considered  most  harmful  at  rolling  temperatures,  | 
since  during  this  process  the  steel  is  liable  to  crack.  Steel  em- 
ployed in  places  where  it  is  exposed  to  corrosion,  must  have  all  the 
sulphur  removed,  since  sulphur  promotes  corrosion  rapidly. 

In  the  present  day  manufacture  of  steel  in  the  United  State i 
sulphur  and  phosphorus  are  removed  by  the  Basic  Open  Hearth  process, 
while  in  England  and  Germany,  these  elements  are  eliminated  by  the 
Basic  Bessemer  process,  the  difference  in  choice  of  the  two  processes 
being  attributed  to  the  contents  of  the  raw  materials  found  in  the 
above  three  countries. 

10 

In  the  Open  Hearth  process,  the  sulphur  and  phosphorus, 
also  silica  with  several  other  impurities,  are  removed  by  the  slag. 
Steel  scrap  is  spread  over  the  bottom  of  the  furnace;  this  is  covered 


V 


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8 


with  a heavy  charge  of  lime,  and  the  lime  is  covered  by  a charge  of 
scrap  and  pig  iron.  After  two  hours,  the  heat  of  the  furnace  has 
softened  this  charge  so  that  it  has  sunk,  and  then  the  final  charge 
of  scrap  and  pig  are  added.  In  order  that  the  slag  may  at  all  times 
be  rich  in  lime,  small  amounts  are  added  from  time  to  time  accord- 
ing to  the  impurities  present.  The  limit  of  GaO  to  be  added  is  55^, 
since  more  than  this  amount  will  form  a viscous  infusible  slag.  Man- 
ganese, if  present,  also  assists  in  the  removal  of  sulphur  by  forming 
MnS.  The  sulphur  in  this  case  is  slowly  oxidized  and  the  manganese 
returns  to  the  boiling  solution  of  metal. 

By  the  Basic  Bessemer  process,  the  sulphur  and  phosphorus 
are  removed  during  the  afterblow  period,  which  is  carried  on  in  a 
converter.  The  converter  is  supplied  with  the  molten  metal  and  is 
blasted  for  a certain  length  of  time  depending  upon  the  amount  of  im- 
purities present.  Lime  is  added  in  amounts  sufficient  to  oxidize  all 
the  impurities.  Some  sulphur  is  oxidized  during  the  blow  and  the  re- 
mainder passes  into  the  slag  in  the  form  of  CaS. 


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EXPERIIffiNTAL . 

On  account  of  the  method  of  manufacture  of  calcium  carbide 
it  most  usually,  as  previously  stated,  contains  impurities.  The 
first  step  in  the  experimental  work  is  therefore  to  ascertain  the 
purity  of  the  carbide,  since  it  is  to  be  used  throughout  this  prob- 
lem. 

An  exact  amount  of  carbide  was  weighed  out  and  placed  in  a 
dry  flask.  As  shown  in  the  diagram,  the  flask  was  connected  with  a 


dropping  funnel,  two  CaClg  U-tubes  and  a train  of  flasks.  The  drop- 
ping funnel  was  filled  with  a 2(y%  brine  solution. 


G'Cn.ftra.t’or  Trap  MaOO  A<mw>oniOwCoJ  ^o\o+ion.  of  CoCi 


The  gas  was  liberated  by  allowing  the  brine  to  drop  on  the  carbide 
verj'"  slowly,  and  when  the  reaction  seemed  to  cease,  the  generator  was  1 
heated  in  order  to  complete  the  reaction;  a saturated  brine  solution 
was  used  because  acetylene  is  Insoluble  in  it,  and  soluble  in  water. 
The  first  U-tube  served  to  remove  the  moisture  from  the  air  current, 
which  swept  the  non-absorbed  gases  into  the  solutions.  The  second 
U-tube  served  to  catch  the  entrained  moisture  in  the  acetylene.  The 
trap  was  employed  to  regulate  the  passage  of  the  gas  in  the  train  of 
flasks,  of  which  the  first  contained  sodium  hypochlorite  to  reraove 
the  hydrogen  sulfide  and  phosphide,  and  the  following  four  flasks  con- 


10 


tained  an  ammoniacal  solution  of  cuprous  chloride  to  absorb  the  acet- 
ylene, by  forming  copper  acetylide.  This  last  compound  is  explosive 
when  dry;  but  it  can  easily  be  dissolved  in  hydrocldoric  acid,  after 
completing  the  experiment.  The  hypochlorite  flask  v/as  weighed  sepa- 
rately, and  the  four  cuprous  chloride  flasks  were  weighed  together, 
before  and  after  the  gas  was  generated.  The  gases  were  determined  by 
gain  in  weight  of  their  respective  absorbing  solutions;  from  five  sue  i 
edeterminations  the  carbide  was  calculated  to  be  pure. 

The  iron  sulphide  to  be  used  in  this  work  was  also  analyzed 
for  its  purity,  by  titrating  against  a standard  solution  of  KMn04. 

An  average  of  four  results  showed  the  PeS  to  contain  61.6^  iron,  but 
since  it  should  theoretically  contain  iron,  this  compound  is 

only  97.24^  pure. 

To  determine  the  value  of  calcium  carbide  as  a metallurgi- 
cal reducing  agent,  I have  centered  all  my  work  on  its  desulphuriz- 
ing effect  on  iron  sulphide,  because  this  is  the  most  common  form  of 
sulphur  occuring  in  steel.  To  begin  with,  the  following  would  be  the 
most  probable  reaction  that  would  take  place  by  heating  the  two  com-  j 

I 

pounds  at  a high  temperature,  assuming  that  the  reaction  would  go  to  | 
completion: 

3CaC2  + 3?eS  = 3CaS  ♦ ^630  + 5C. 

Since  equal  moles  of  the  carbide  and  sulphide  are  necessary  for  the 
reaction,  as  indicated  by  the  equation,  one- fourth  the  molecular 
weights  of  each  (considering  their  purity)  were  v/eighed  accurately 
and  mixed  thoroughly;  22.5625  grams  FeS  and  35.55  grams  CaC2.  This 
mixture  was  placed  in  a fire  clay  crucible  and  heated  in  a small  pot 
furnace  for  four  hours  at  a constant  temperature  of  1000®C.  The  re- 
sulting mass,  formed  one  large,  rather  brittle  lump,  but  did  not  fuse 
enough  to  pour.  It  was  pulverized  to  a fine  powder  in  an  iron  mortar 


■*j‘ ’<  U'  *..1*1. 


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11 


during  which  time,  necessary  precautions  were  exercised  to  prevent 
any  loss  of  the  fine  material. 

Half  of  this  pulverized  mass  was  divided  into  two  equal 
portions,  and  analyzed  for  the  presence  of  free  calcium  carbide.  The 
same  method  and  apparatus  used  for  the  determination  of  the  purity  of 
the  carbide,  described  in  the  beginning  of  the  experimental  ?/ork,  was 
employed  here.  I wish  to  say,  that  all  the  results  on  this  and  fol- 
lowing pages,  are  the  best  checks  selected  from  analyses  of  four  fu- 
sions, all  the  fusions  being  made  under  the  same  conditions  and  treat 
ments;  of  course  the  results  were  taken  from  only  one  of  the  four  com 
plete  analyses,  and  is  not  a collection  of  results  taken  from  parts 
of  each  complete  analysis. 

Determination  of  free  Calcium  Carbide. 

1 2 

10.0275  gm.  sample  used  10.0275  gm.  sample  used 

.8151  gms . G2H2  liberated^  .8090  gms . C2H2  liberated= 

2.007  gms.  free  CaC2  1.99  gms.  free  CaC2 

since  the  sample  used  is  only  l/4  the  total  sample,  the  total  free 

CaC2  is  equal  to: 

8.028  gras.  7.960  gms. 

average  value  = 7.994  gms. 

Sixteen  grams  of  pure  carbide  were  used  to  make  the  fusion, 
and  the  analysis  indicate  that  only  7.994  grams  remained.  The  miss- 
ing carbide  may  have  been  dissipated  in  several  v/ays;  in  the  forma- 
tion of  CaS,  CO2,  CaO,  or  C.  From  the  following  investigation,  we 
can  conclude  that  some  of  the  carbide  was  used  in  the  formation  of 
CaS.  The  assumed  CaS  was  washed  out  of  a five  gram  sample  of  the 
fusion  with  several  portions  of  boiling  water,  and  the  remaining  res- 
idue was  carefully  dried,  and  later  analyzed  for  its  sulphur  contents 


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in  the  form  of  FeS.  Since  CaS  is  hydrolized  by  water,  reacting  in 
this  manner, 

CaS  + 2H2O  = Ca(0H)2  + H2S 

the  above  washings  contained  Ca(0H)2in  place  of  CaS.  During  the  hy» 
drolysis,  a distinct  odor  of  H2S  was  detected,  which  verifies  the  a- 
bove  reaction  and  the  presence  of  CaS  in  the  fusion.  To  verify  the 
presence  of  Ca(0H)2»  the  washings  were  treated  with  Na2C204,  and  a 
white  characteristic  precipitate  of  CaC204  was  formed.  The  detection 
of  the  H2S  odor  during  hydrolysis  is  more  conclusive  evidence  of  the 
existence  of  CaS,  than  is  the  oxalate  precipitate,  since  the  latter 
may  have  been  formed  from  the  Ca(OH)g  produced  by  the  decomposition 
of  the  carbide  by  the  water,  or  from  the  CaO  which  exists  as  an  im- 
purity in  the  carbide  in  unknown  quantities. 

I 

I 

i 

Determination  of  the  FeS  reduced. 

i 

Analysis  of  the  above  Five  Gram  Sample  from  which  the  CaS  has  been  | 

thoroughly  removed:  | 

! 

The  sulphur  v/as  oxidized  to  sulphuric  acid  by  fusion  with  30  grams  of  | 

pure  sodium  peroxide  in  a nickel  crucible.  This  fusion  was  thorough-  ! 

ly  washed  out  into  a beaker,  filtered,  and  treated  with  BaCl^,  to  pre- 1 

cipitate  the  sulphur  as  BaS04: 

1 2 

6.5698  gms.  BaS04  6.5253  gms,  BaS04 

Sulphur  equivalents .904  gms.  Sulphur  equivalent^  .897  gms. 

PeS  *•  =2.479  FeS  “ =2.461  " 

FeS  in  total  fusion  consisting  of  40.1102  grama; 

19.85  gms.  19.72  gms. 

average  value=19.785  gms.  FeS  present. 

22.5625  gms. FeS,  which  is  equivalent  to  21.92  gms.  pure  FeS,  were  usee 

in  making  the  fusion;  therefore 

21.92-19.25=2,135  gms.  or  9.74^  of  the  FeS  was  reduced. 

The  above  results  indicate  a very  low  efficiency  of  calcium 
carbide  as  a desulphurizing  agent;  thus  the  carbide  has  no  practical 


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13 


value  for  the  purpose  intended  under  the  administered  treatment. 

Therefore  this  investigation  was  further  carried  on  by  heat, 
ing  the  same  quantities  of  carbide  and  sulphide  (35.55  gms.  and 
22.5625  gms.  respectively)  in  a fire  clay  crucible.  The  temperature 
was  kept  constant  at  1200°  for  four  hours  by  the  use  of  a gas  pot  fur- 
nace. The  product  obtained  was  a fused  mass,  of  what  appeared  to  be 
only  iron,  being  much  less  brittle  than  the  product  obtained  by  the 
1000°  heat,  and  also  had  less  free  calcium  carbide  distributed  over 
the  surface.  This  was  treated  and  analyzed  in  the  very  same  manner 
as  the  previous  fusion,  and  the  following  are  the  results: 


Determination  of  Free  Carbide. 

1 2 

9.2436  gm.  sample  used  9.2436  gm.  sample  used 

.3624  gms.  CgH2  liberated=  .3685  gms.  liberated^ 

.8932  gms.  free  CaCp  .9079  gms.  free  CaCp 

This  being  only  one- fourth  of  the  total  sample,  the  total  free  carbid« 
will  then  be: 

3.5728  gms.  3.6316  gms. 

average  = 3.6022  gms.  free  carbide. 


Determination  of  the  FeS  reduced. 

1 2 

5.5885  gms.  BaS04  5.5598  gms.  BaSO. 

Sulphur  equivalent  = .768  gms.  Sulphur  equivalent  = .764  gms. 

" = 2.107  gms.  PeS  ” = 2.095  gms. 

PeS  in  total  fusion  consisting  of  36.9744  gms.: 

15.583  gms.  PeS  15.499  gms.  PeS 

average  value  = 15.541  gms.  PeS  present. 

22.5625  gms.  PeS,  which  is  equivalent  to  21.92  gms.  pure  PeS,  were 
used  in  making  the  fusion;  therefore 

21.92  - 15.541  = 6.379  gms.  or  29.152^  of  the  PeS  reduced. 

By  comparing  the  last  results  with  those  obtained  by  the 
1000°  fusion,  we  can  almost  conclude  that  at  higher  temperatures  the 
reducing  effect  of  the  carbide  is  increased.  But  there  must  be  some 
definite  temperature  at  which  all  the  carbide  will  enter  into  the  re- 


14 


action,  and  It  is  obvious  that  at  this  temperature,  the  total  reduc- 
ing power  of  the  carbide  will  be  consummated.  With  this  point  of 
view,  another  fusion  was  made  employing  the  same  quantities  of  car- 
bide and  sulphide  as  used  in  the  two  previous  fusions.  The  tempera- 
ture was  kept  at  1400®  C for  one  and  a half  hours  by  means  of  an  oil 
pot  furnace.  At  this  high  heat  it  was  necessary  to  use  a graphite 
crucible,  the  inside  of  which  was  lined  with  a smooth  layer  of  fire 
clay.  A hard,  black,  glossy,  slag  and  a mass  of  iron  was  produced. 
The  silica  contained  in  the  crucible  lining  also  took  part  in  the  re- 
action, by  helping  in  the  slag  formation.  This  last  statement  sug- 
gests the  thought,  that  the  addition  of  silica  would  probably  lower 
the  reaction  temperature  and  lessen  the  time  of  operation,  but  this 
thought  is  contradicted  by  the  fact  that  the  lower  temperature  fus- 
ions (lOOO®  and  1200®)  were  carried  out  in  fire  clay,  silica  contain- 
ing crucibles  which  were  not  even  slightly  attacked  after  four  hours 
of  continuous  heating.  These  crucibles  contain  71.81^  silica,  most 
of  which  would  have  readily  taken  part  in  the  reaction  if  there  were 
need  for  it,  as  it  was  with  the  1400®  fusion. 

An  analysis  of  the  mass  of  iron  was  made,  for  the  determin- 
ation of  free  calcium  carbide,  but  not  a trace  could  be  detected. 
Applying  the  same  method  used  in  the  previous  analyses,  the  quantity 
of  unreduced  FeS  was  determined. 

1 2 

5 gm.  sample  used  5 gm.  sample  used 

7.1023  gms.  BaS04  7.1893  gms . BaS04 

Sulphur  equivalent  = .977  gms.  Sulphur  equivalent  = .979  gms. 

PeS  ” = 2.679  gms.  5*63  **  = 2.682  gms. 

PeS  in  total  fusion  consisting  of  19.6385  gms.: 

10.51  gms.  10.54  gms. 

average  = 10.525  gms.  PeS  present. 

22.5625  gms.  PeS,  which  is  equivalent  to  21.92  gms.  pure  PeS,  were 
used  in  making  the  fusion;  therefore 

21 .92-10i»525  = 11.395  gms.,  or  52^  of  the  PeS  was  reduced. 


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15 


SUMIJIARY. 

Since  at  1400°  C,  all  the  calcium  carbide  takes  part  in  the 
reaction  in  one  form  or  another,  it  is  evident  that  at  this  tempera- 
ture the  carbide  produces  its  greatest  reducing  effect  on  ferrous 
sulphide.  Higher  temperatures  may  shorten  the  time  of  operation,  but 
I doubt  whether  higher  temperatures  would  be  employed  commercially 
for  this  purpose,  because  high  heats  tend  to  decrease  the  life  of  any 
furnace  considerably. 

The  presence  of  silica  is  necessary  for  the  formation  of  a 
running  slag,  which  is  a very  important  factor  in  large  scale  work. 

With  an  efficiency  of  52^,  as  the  results  indicate,  the  use 
of  calcium  carbide  as  a reducing  agent  for  iron  sulphide  is  not  prof- 
itable on  account  of  the  high  cost  of  the  carbide.  If  a much  cheaper 
method  for  the  manufacture  of  carbide  is  developed,  this  process  of 
reducing  iron  sulphide  could  be  advantageously  used  on  a commercial 
basis. 

The  reducing  efficiency  of  calcium  carbide  cannot  be  entire- 1 

I 

ly  judged  by  its  effect  on  ferrous  sulphide  alohe,  since  it  may  rendei 
a greater  efficiency  in  reducing  oxides,  other  sulphide  ores,  and  sul- 
phur in  steel  and  pig  iron.  Two  other  men  who  are  independently  en- 
gaged in  investigations  similar  to  this,  have  found  that  calcium  car- 
bide reduces  from  35  to  55^  of  sulfur  in  steel,  and  also,  that  the  re- 
action of  carbide  with  ferric  oxide  begins  at  1250°  C and  is  completec 
at  1500°  C. 

The  efficiency  of  52^  as  indicated  by  the  experimental  re- 
sults, does  not  take  into  consideration  any  sulphur  that  may  have  beer 
oxidized  to  sulphur  dioxide.  In  this  light,  the  52;^  efficiency  is  too 


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K(  ' ? -fojiii. 


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high.  In  order  to  determine  the  efficiency  correctly,  the  amount  of 
sulphur  present  in  the  slag  must  he  determined.  In  the  lower  temper- 
ature fusions  (at  1000°  and  1200°)  in  which  the  reduced  sulphur  is  in 
the  form  of  calcium  sulphide,  the  sulphur  may  he  determined  hy  ab- 
sorbing the  hydrogen  sulphide  in  lead  acatate  during  the  hydrolysis 
of  the  calcium  sulphide;  this  reaction  is  explained  under  the  analysii 
of  the  first  fusion.  If  more  time  were  available,  I would  have  made 
the  above  quantitative  determinations  of  sulphur. 

This  problem,  therefore,  still  has  a momentous  field  open 
for  investigation,  which  I hope  will  be  further  continued  by  those 
whose  interest  may  have  been  aroused  by  this  article. 

I regret  that  I have  only  had  one  half  year  (one  semester) 
to  spend  on  this  tremendous  task  and  that  so  little  could  be  accomp- 
lished, but  I feel  that  the  time  was  well  spent,  if  this  article  will 
only  give  an  impetus  towards  the  completion  of  this  investigation. 


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BIBLIOGRAPHY. 

1 Calcium  Carbide  and  Acetylene  by  Fowler,  P 665 

2 J.  S.  C.  I.  1895,  Page  440. 

3-4  Calcium  Carbide  and  Acetylene  by  Fowler,  P 665 
5 J.  S.  C,  I.  1897,  Page  145. 

5-6  Chemical  News,  Volume  75,  Page  2. 

7 J.  S.  C.  I.  1901,  Page  46. 

8 J.  S.  C.  I.  1900,  Page  475. 

9 Transactions  of  the  American  Society  for  Steel  treating. 
Volume  1,  January  1921. 

10  The  Metallurgy  of  Iron  and  Steel  by  Bradley  Stoughton. 


